1. Field of the Invention
Embodiments of the present invention relate to a soft mold, and more particularly, to a method of fabricating a soft mold with the improved interfacial properties between the soft mold and a substrate including a pattern-formation material and a method of forming a thin film using the same.
2. Discussion of the Related Art
A fine-pattern formation process, for example, a process for forming an electric circuit is an important element which can determine the efficiency and capacity of device as well as a main element which can affect the properties of device.
Recently, there are various efforts to improve the efficiency and capacity of device, and more particularly, studies and researches in relation with the formation of fine pattern so as to improve the efficiency and capacity of device.
The fine-pattern formation process is necessary for flat panel display devices such as a printed circuit board (PCB), a liquid crystal display device (LCD), and a plasma display panel (PDP).
Various studies for formation of the pattern have been made, especially, a photolithography process using a photoresist is most generally used, which will be described as follows.
First, a photoresist layer having photosensitivity is coated on a metal layer, wherein the metal layer is formed on a substrate of a semiconductor material or an insulation material such as glass.
Then, a soft baking process is applied to the photoresist layer.
After an exposure mask having a light-transmission region and a light-shielding region defined therein is positioned above the photoresist layer, UV rays are applied to the photoresist layer through the exposure mask. Generally, the photoresist may be classified into a positive type and a negative type. For convenience of explanation, the case using the negative type photoresist will be explained as follows.
If UV rays are irradiated to predetermined portions of the negative type photoresist, the predetermined portions of the negative type photoresist, which are irradiated with the UV rays, are changed on their chemical structure.
Then, if the negative type photoresist is dipped into a vessel filled with a developer, a photoresist pattern is formed by removing the remaining portions of the negative type photoresist which are not irradiated with the UV rays.
Subsequently, after blocking some of a metal layer with the photoresist pattern, it is dipped into the developer. Then, a hard baking process is applied thereto, and then the metal layer except the portion below the photoresist pattern is etched to thereby form a metal pattern.
According as the photoresist pattern is removed by a stripper, only the metal pattern remains on a substrate.
At this time, a semiconductor layer, an insulation layer or other conductive layers instead of the metal layer may be etched.
However, the related art fine-pattern formation method using the photoresist has the following disadvantages.
First, the process becomes complicated due to the resist coating, the soft and hard baking for the coated resist, and the exposure and development. Furthermore, for baking the photoresist, it necessarily requires both the soft baking performed at a first temperature, and the hard baking performed at a second temperature which is higher than the first temperature of the soft baking, which causes the more complicated process.
Also, the fabrication cost is increased. In general, the process for the electric device including a plurality of patterns (or electrodes) is provided with a first photoresist step to form one pattern and a second photoresist step to form another pattern. This means that the expensive resist process line is required between each of the pattern lines. Thus, the fabrication cost for the electric device is increased.
Third, it may cause environmental contamination. Since the resist coating is generally performed by spin coating, the amount of resist disused on the coating process is increased, whereby it may cause the environmental contamination as well as the increasing fabrication cost.
Fourth, there are the defective devices. When forming a resist layer by the spin coating, it is difficult to control the precise thickness of resist layer. Accordingly, the thickness of resist layer is not uniform so that un-stripped resist portions remain on the surface of the pattern formed, thereby causing the defective devices.
In order to overcome the problems of the above-mentioned patterning method using photolithography, a new patterning method using a soft mold will be explained as follows.
First, a master is prepared so as to obtain a predetermined shape in a surface of a soft mold by an embossing or depressed pattern.
For example, a primary layer is formed by depositing an insulation material such as silicon nitride Si3N4 or silicon oxide SiO2 on an insulation substrate such as silicon substrate. Then, a photolithography process is applied to the primary layer, whereby the primary layer is formed as a desired pattern.
At this time, the above-mentioned pattern of the insulation substrate may be formed of metal, photoresist or wax as well as silicon nitride or silicon oxide. Through the above-mentioned process, the master is completed.
On completion of the master, a pre-polymer layer is formed on the master.
Then, the pre-polymer layer is cured.
Next, the cured pre-polymer layer is referred to as a soft mold. As the soft mold is stripped off from the master, the embossing and depressed pattern is formed in the surface of the soft mold.
The soft mold is used to form a micro-unit fine pattern (pattern formed by the embossing or depressed shape of the soft mold). For example, the soft mold may be used for a color filter of a color filter substrate or an electrode of an OLED device.
The soft mold may be fabricated by curing an elastic polymer, for example, PDMS (polydimethylsiloxane) typically. In addition to PDMS, polyurethane or polyimide may be used.
The soft mold may be applied to various fields of soft lithography, soft molding, capillary force lithography and In-Plane printing.
Hereinafter, a patterning method using a mold according to the related art will be described with reference to the accompanying drawings.
FIGS. 1A to 1D are cross section views of illustrating a method of forming a pattern according to the related art.
As shown in FIG. 1A, a first material layer 11 is deposited on a substrate 10, and a pattern material layer 12 for a desired pattern is coated on the first material layer 11 by an inkjet apparatus or a dispenser 20.
Referring to FIG. 1B, a soft mold 31 is comprised of a lower surface of flat type and an upper surface having embossing and depressed shapes. The soft mold 31 is positioned above the pattern material layer 12. Also, the lower surface of flat type of the soft mold 31 is put on a backplane 30.
As shown in FIG. 1C, after aligning the soft mold 31 and the substrate 10, the upper surface of the soft mold 31 is brought into contact with the pattern material layer 12, whereby the embossing and depressed shapes of the soft mold 31 are stamped on the pattern material layer 12. As a result, the depressed shapes of the soft mold 31 remain on the pattern material layer 12, thereby forming a pattern layer 12a. At this time, in state of that the soft mold 31 is brought into contact with the pattern material layer 12, the pattern material layer 12 is cured by ultraviolet rays UV. In another aspect, the pattern material layer 12 may be cured by heat.
As shown in FIG. 1D, the soft mold 31 is separated from the surface of first material layer 11 provided with the pattern layer 12a. 
FIGS. 2A and 2B illustrate shrinkage of resin after aligning the soft mold and the substrate in the method of forming the pattern according to the related art.
As shown in FIG. 2A, the pattern material layer 12 such as resin is coated adjacent to the edge of the first material layer 11 on the substrate 10. Then, the contact process shown in FIG. 1C is carried out between the substrate 10 and the soft mold 31. Since the soft mold 31 and the pattern material layer 12 have the different interfacial properties as shown in FIG. 2B, the pattern material layer 12 positioned at the circumference may shrink due to the repulsive force of soft mold 31 and the surface tension of pattern material layer 12, whereby the deformation (12x) of pattern material layer 12 may occur.
If the deformation (12x) of pattern material layer occurs, it may cause the failure of contact between the soft mold 31 and the circumferential part of pattern material layer corresponding to the deformation (12x). As a result, it is difficult to realize patterning of the pattern material layer with the uniform thickness, thereby causing the defective pattern.